1. Field of the Invention
The invention relates to a control unit for a motor vehicle
2. Description of the Related Art
Recently there has been an increasing tendency to integrate the engine control units and the transmission control units into the motor vehicle assembly (i.e. engine or transmission) to be controlled. This concept has a considerable potential to save costs in comparison to the conventional use of external control units. Technological difficulties arise owing to increased system requirements such as being leak proof with respect to ambient media (oil, gasoline, water), operational capability over a wide temperature range (for example xe2x88x9240xc2x0 C. to 150xc2x0 C.) and resistance to abrasions (up to approximately 40 g).
A control unit described in German patent DE 197 12 842 C1 has an electrical connection between the control electronics and the electrical components to be controlled realized by a flexible printed circuit board. It has been found that it may occasionally be difficult to ensure a defined course of the flexible printed circuit board outside the control unit.
In German patent application DE 195 15 622 A1, a transmission control unit is described in which the electrical contact with the electrical components actuated by the control unit are formed by a punched grid which is injection molded in the plastic lid part of the control unit. This solution permits contact to be made with the electrical components in a mechanically stable and electrically secure way, but it is relatively complex in structural terms. Another motor vehicle control unit is described in German patent DE 197 34 032 C1.
German laid-open application DE 42 28 818 A1 describes a control unit for motor vehicles in which a flexible printed circuit board is led between a base plate and an inner sealing frame in a seal-forming fashion to a housing plug. The electrical connection of the motor vehicle control unit to external electrical components is made via the housing plug.
In German laid-open application DE 44 37 664 A1, a motor vehicle control unit is described which has a housing body formed of a curable foam. A plurality of flexible printed circuit boards project out of the housing body and form connections to electrical components located in the vicinity.
The invention is based on the object of providing a control unit for a motor vehicle which permits external electrical components (plugs, actuators, sensors) to be electrically connected to the control electronics of the control unit in a way which can be implemented cost-effectively and is mechanically secure.
The object on which the invention is based is achieved by having the printed circuit board carrier structure continue the base plate in a planar fashion, so that a course of the flexible printed circuit board outside the control unit is sufficiently positionally defined in accordance with the structural circumstances . As a result, mechanical damage to the flexible printed circuit board, such as may occur, for example, owing to vibrations due to friction of the printed circuit board against adjacent walls or engine/transmission components, can be reliably avoided.
The use of a flexible printed circuit board for distributing current makes possible significant cost advantages in comparison to solutions which are structurally more complex (cabling with plug-type connectors, punched grids integrated into housing parts etc.).
The printed circuit board carrier structure is preferably dimensioned in such a way that its outer contour surrounds the outer contour of the flexible printed circuit board essentially on all sides. The flexible printed circuit board is then covered over its entire surface by the printed circuit board carrier structure and its position can be controlled via the latter at virtually any point.
The printed circuit board carrier structure can preferably include disconnectable sections and/or sections which extend in various planes. This permits the specific advantages of a flexible printed circuit board in terms of the compensation of mounting and component tolerances to continue to be used.
In principle, the flexible printed circuit board can be held in the desired, defined position solely by bearing against the printed circuit board carrier structure. However, in a particularly advantageous variant of the invention the flexible printed circuit board is secured locally to the printed circuit board carrier structure at specifically predefined positions. This permits the flexible printed circuit board to be positioned and aligned precisely on the printed circuit board carrier structure, which facilitates the mounting of the composite structure, composed of the printed circuit board carrier structure and printed circuit board, in the transmission/engine. By selecting suitable securing positions it is possible to ensure that the printed circuit board cannot be damaged owing to different degrees of expansion of materials even when there are very large fluctuations in temperature.
The preferably metallic base plate may be anchored in a depression or opening in the printed circuit board carrier structure which is preferably composed of plastic.